Identifying the genetic changes underlying adaptive phenotypic change is a fundamental challenge in evolutionary biology. While mapping approaches have been useful for detecting regions of the genome affecting trait variation, pinpointing the specific changes responsible at the DNA sequence level remains difficult, unless candidate genes within the region are known. This project uses a candidate gene approach to identify the genetic changes involved in adaptive transitions in flower color in lochroma, a genus in the tomato family, Solanaceae. Flower color is an ideal trait for studying the genetic basis of adaptation because it has clear adaptive significance and because the pigment biosynthetic pathways are well- characterized at the genetic level and highly conserved across flowering plants. Color differences among lochroma species are largely due to differences in anthocyanin pigments, a class of flavonoids. The proposed research will investigate the genetic changes in the anthocyanin pathway responsible for the evolutionary transition from purple to white flowers in I. loxense and from purple to red flowers in I. gesnerioides. Combining the detailed understanding of the pathway and knowledge of which pigments are present in the study species, strong predictions can be made about which anthocyanin genes were involved in the color transitions. The association of candidate anthocyanin genes and color differences will be assessed by (1) examining the cosegregation of candidate genes with flower color phenotypes in interspecific crosses between red, white, and purple species, (2) cloning candidate genes showing cosegregation to test their functionality in vitro, and (3) using expression studies to examine possible differences in regulation. The results will help to address basic questions regarding the number, location and types of genetic changes involved in the process of adaptation. Furthermore, this research may serve as a model for studying the evolution of biochemical pathways, which in turn, has broad implications for human health, from gene therapy to improved drug targeting. In addition, flavonoids (including anthocyanins) have well-known antioxidant activity, which appears to aid in preventing chronic diseases, such as heart disease and cancer. Thus, a better understanding of how genetic changes alter enzyme action in the flavonoid pathway adds to our potential for improving crop species.